Water may be properly taken from ponds or lakes whenever the danger from pollution is negligible. No better source of supply can be imagined than a pond in the midst of woods, far away from human habitation, presumably furnishing an unlimited supply of pure soft water. Sometimes water from such ponds contains large amounts of vegetable matter, the result of decomposition of swampy or peaty material, as, for instance, from the ponds in the Dismal Swamp of Virginia, so that the water has a yellow, coffee-colored appearance. The appearance of such water is suspicious, but it need not be feared unless something more pernicious than the coloring matter is present.
As the country becomes more settled, ponds are more and more likely to become contaminated and hence unfit for a water-supply, and this possibility must be taken into account in planning for a water-supply. It would be most shortsighted to carry a long line of pipe from a house to a pond several miles away, only to have the pond made unfit for use within a few years by the growth of the community around the pond. The possibility of coöperation ought not to be overlooked, however. It is quite possible that half a dozen householders might be so located with respect to each other and to a pond that an arrangement could be made whereby the owner of a small pond would agree to fence it around and dedicate it to the purposes of a water-supply, doing this as his share. The others might then well afford to pipe the water to one house after another, including that of the owner of the pond.
Water from a pond or lake has one great advantage over water from a brook, namely, that contaminating substances in the pond settle out, so that pond water, especially if the pond is deep, is always of much better quality than running water. For this same reason, water taken from a reservoir on a stream is much better water than that in the stream above the reservoir indicates, and pollution is much less to be feared where the reservoir exists.
Pressure for water-supplies.
The value of a high pressure in the water-pipes of a house has been much overestimated. For a number of years the water-supply in the writer's residence came from a tank in the attic, the pressure in the bath-room being not more than ten feet, and while the water flowing through a three fourths inch pipe was noticeably slow, it was not so slow as to discredit the supply.
A height or head of twenty feet above the highest fixture in the house would be better and ought to be secured whenever possible. This head is obtained by having the source of supply higher than the highest fixture, not merely the twenty feet mentioned, but also an additional height necessary to offset the frictional losses caused by the running water. The loss from this source in case of fire supply has already been referred to, but for purely domestic supplies the loss is appreciable. The maximum rate as already indicated is not more than 7000 gallons per day, whereas the fire rate both for single houses and for a small hamlet is about a million gallons a day. For the lower rate, as well as for rates one half and twice this rate, the friction loss in vertical feet per 100 feet run in small pipes is shown in the following table:—
Table X. Showing Loss of Head by Friction, for Different Quantities of Flow, and in Different Sizes of Pipes
| Rate of Flow in Gallons Per Day | 1/2" Pipe | 5/8" Pipe | 3/4" Pipe | 1" Pipe | 1-1/4" Pipe |
| 3500 | 13.95 | 4.81 | 2.35 | 0.66 | 0.25 |
| 7000 | 47.17 | 17.30 | 7.45 | 2.04 | 0.74 |
| 14000 | 163.09 | 57.8 | 25.00 | 6.64 | 2.41 |
The table shows how much additional elevation is needed over the 20 feet already referred to. For example, suppose it is decided that a rate of 1 quart in 10 seconds is to be maintained from three faucets or a rate of 7000 gallons per day. Suppose that a pond 4000 feet away is found to be 50 feet above the highest faucet in the house, and it is a question what size pipe ought to be used. By the table a 1-inch pipe loses 2.6 feet per 100 feet or 104 feet in the 4000 feet, an impossible amount when only 50 feet are available, although the size would be entirely proper if the difference of level was 124 feet or anything greater. A 1-1/4-inch pipe, however, loses only 0.74 foot in 100 or 39 feet per mile, so that the 1-1/4-inch pipe would be necessary, although that size would answer even if the pond were a mile and a quarter away.
When water from a well is pumped to an elevated tank there is the same necessity of providing about 20 feet difference in level between the tank and the highest fixture, but the length of pipe involved being small, the friction losses are not great. It should be noted even here that too small a pipe may reduce the pressure, a 1/2-inch pipe causing a loss of 47 feet in a 100-foot pipe line. If a tower is built by the side of the house, the distance down to the ground, across to the house, and up to the second floor would hardly be less than 50 feet, and this is a loss of 23-1/2 feet, which means that the tank would have to be set higher in the air by this amount. With a 3/4-inch pipe, it should go 3.7 feet, and with a 1-inch pipe but a foot higher than the level necessary to make the water flow out of the faucet at the rate already specified.